Are the playlists you’re trying to add to Smart playlists, based on filters, or standard playlists that you manually added everything to?
When you manually add an item to a playlist, it only shows standard playlists, because Smart playlists are based solely on the filters you selected when you created the playlist. The only way to add an item to a Smart playlist is to tag the item to fit the playlist’s filter settings. For example, if the smart playlist is based on the filter “genre = Science Fiction,” all you have to do to add a movie to the playlist is to tag it with that genre. It will automatically be added to the playlist.
